1. Field of the Invention
Various penicillin compounds, such a benzylpenicillin (penicillin G), ampicillin, and the like, are collectively the most widely used antibiotics today. Penicillins are the treatment of choice for a wide variety of bacterial infections because, among other reasons, they are inexpensive and widely available.
A number of bacterial strains, however, are resistant to penicillin treatment, producing .beta.-lactamases which inactivate penicillin by hydrolyzing the .beta.-lactam ring. The resulting hydrolyzed compounds (referred to generally as penicilloic acids) display no antibiotic activity.
It would be desirable to provide an assay for measuring the presence of such .beta.-lactamases in human sera. The assay would serve to detect bacterial infection by .beta.-lactamase producing organisms, since mammalian tissues do not normally produce this enzyme. Such an assay would also allow the determination of whether the infection was caused by a penicillin-resistant strain since such strains would tend to elaborate higher levels of .beta.-lactamase than would sensitive organisms.
Direct immunological measurement of .beta.-lactamases, however, is problematic since different bacteria produce .beta.-lactamases which are not immunologically cross-reactive. Because of the convenience of immunoassays in general, it is desirable to devise an immunoassay capable of inferentially measuring the level of .beta.-lactamases present in human sera.
2. Description of the Prior Art
Yolken, et al. (1980) J. Pediatrics 97:715-720, describe a non-immunological radioisotopic assay which measures the presence of .beta.-lactamases based on the conversion of penicillin to penicilloic acid. Immunogens to penicillin are described in Wal, et al. (1975) FEBS Letters 57:9-13; Munro, et al. (1978) J. Pharm. Sci. 67:1197-1204; and Horiughi and Shibata (1965) Int. Arch. Allergy 28:306-320. Each of these articles teaches that immunogens may be formed by hydrolyzing the .beta.-lactam ring of penicillin and conjugating directly to the .epsilon.-amino groups of lysine in the protein carrier. Kitagawa, et al. (1978) J. Biochem. 84:491-494, couple ampicillin to proteins by acylation of the amino group of ampicillin with a functionalized acid and coupling with the protein after reductive cleavage of the disulfide bonds in the cysteine groups of the protein.